For industrial pressure-sensitive adhesive tape applications it is very common to use double sided pressure sensitive adhesive (PSA) tapes in order to bond two materials to one another. For the wide variety of applications the requirements are in some cases highly specific, with the consequence that stringent requirements are imposed on the corresponding adhesive tapes. In the automobile segment, for example, the requirements very often include high temperature stability and a high level of resistance to solvents and fuels. These properties are met in a very good form by crosslinked acrylic pressure sensitive adhesives (acrylic PSAs).
Additionally, again in the industrial sector, a very wide variety of substrates may be bonded. In this case it may sometimes be of advantage to use heat activatable adhesives which soften above a certain temperature, flow very well onto the substrate, and then cool to give a firm bond.
U.S. Pat. No. 6,124,032, for example describes a heat activatable adhesive tape for sealing cartons. The requirements in this segment, however, are very low, since the forces which act on the adhesive tape by the carton are relatively low. This is manifested in the carrier material, which is composed of paper. The focus is therefore not on bond strength but rather on a production process for an expensive PSA tape.
U.S. Pat. No. 5,593,759 describes a double sided PSA tape which is composed of a carrier layer coated with two thin PSAs. The carrier layer is composed of a structural adhesive. On thermal activation, the PSA blends with the structural adhesive and also cures it. In this way, very firm bonds between two adherends are possible. Nevertheless, this PSA tape has an elementary disadvantage for many applications, namely the fact that the double sided PSA tape is tacky on both sides to start with. There exist a large number of applications in which it is advantageous if the PSA tape is nontacky, at least on one side, and hence possesses optimum repositionability. In U.S. Pat. No. 5,593,759 this advantage is absent.
U.S. Pat. No. 4,248,748 describes heat activatable polyacrylate PSAs with additions of resin. The additions of resin raise the glass transition temperature of the polyacrylate PSA and hence the tack at room temperature. The heat activatable PSAs are, however, used only for single sided PSA tapes (film bonding, etc.). Accordingly, the requirements concerning the bonding of adherends or the anchoring of heat activatable PSAs to the film are not high.
U.S. Pat. No. 4,199,646 describes heat activatable PSA tapes where the heat activatable PSA has a modulus of elasticity of from 10 to 300 kg/cm2. The modulus at the activation temperature is therefore at the level of PSAs at room temperature. In this patent as well, in analogy to U.S. Pat. No. 4,248,748, the bond strength and the elasticity are controlled via the composition of the PSA. Moreover, only double sided heat activatable PSA tapes are described, which can be activated by heat only on both sides.
Accordingly there is a need for an adhesive tape which, by virtue of its construction and the adhesives used, is suitable for bonding different materials to one another in specific fields of application.